This invention relates to an improved process for the selective hydrogenation of acyclic and cyclic carboxylic acid anhydrides to esters and lactones. More particularly, this invention relates to the selective conversion of said anhydrides to esters and lactones respectively hydrogenating hydrogenating them under mild conditions in the presence of an organometallic ruthenium complex catalyst in homogeneous solution.
It is known, for example, from Kanetaka et al., Japan 71, 33,030, that succinic anhydride can be hydrogenated to .gamma. -butyrolactone using heterogeneous catalysts which necessitate vigorous conditions: 2000.degree.-300.degree.C., 1500-3000 psi H.sub.2. Reaction is unselective and tetrahydrofuran is usually formed as a by-product.